Here are O-C diagrams for a selection of Mira stars. The diagrams shows the cycle number (E) on the x-axis and O-C in days on the y-axis. The red dots are maxima that are fitted from observations, the lightblue are maxima published by AAVSO and the darkblue are maxima collected from various other published sources. The fitted maxima are based on observation data from the organizations AAVSO, AFOEV, VSOLJ and BAA/VSS and calculated by using a mean lightcurve for each star. The mean lightcurves used can be found here. For a maxima to be recognized it had to fulfil these criteria:
- At least 12 observations around the maximum.
- At least 5 observations before and 5 observations after the peak observation.
- At least an amplitude of 1.5 magnitudes between the peak observation and the observations before and after.
- Only observations in a span of 80% of the variable's period around the peak observation is used.
When a maximum fulfilling the criteria was found the mean lightcurve was fitted to the observations and the time and magnitude was noted. A preliminary O-C was then calculated by using the elements from GCVS4. In some cases a manual correction of the O-C was needed if the O-C is out of phase with more than a half cycle. From these O-C values an adjusted mean period and epoch was derived and new O-C values were calculated and plotted in the diagrams below.
The AAVSO maxima have been adjusted with a fixed offset for each star to get the datasets in line with each other.

By clicking on the graph a table with the underlying data is presented.

Under each graph are some data about the star and the diagram.
The 1st row shows the new mean period and epoch. LC is a link to the mean lightcurve for the star. Avg is a link to a smoothened O-C diagram constructed by using a moving average of 7 points around each point in the original diagram. Per is a link to a diagram that shows the star's period over time.
The 2nd row shows the result of an linear fit to the GCVS4 O-C values. ΔP is the slope in days/cycle. The GCVS4 period is added by this amount to get the new mean period. The ± is the standard error for the coefficient. t: is the t-statistics (ΔP / standard error) and suggest the significance of the linear fit, r2: shows the coefficient of determination for the fit. ΔEpoch is the interception point with the y-axis. The GCVS4 epoch is adjusted by this amount to get the new mean epoch.
The 3rd row shows the same thing but for a parabolic fit. A parabolic O-C diagram suggest that the period is changing in a steady pace and ΔP/C shows the amount in days per cycle that best fit the diagram. Care should be taken not to overestimate this information as most O-C diagram shows a lot of random scatter in the period that can create false relations. Stars with a high value of t: and a r2: near 1 could be candidates for Miras with a continuous changing period.
The colour for ΔP and ΔP/C is red for t: <5 and green for t: >= 5 to easier see where there is a high statistically significance. ΔP and ΔP/C is also clickable. ΔP shows a diagram with the original GCVS4 elements and ΔP/C shows the residuals when the parabolic part of the curve is removed.
The 4th row shows the mean magnitude at max ± standard deviation. The extreme values are showed within parentheses.
The 5th row shows the original period and epoch from GCVS4.
The 6th row shows the spectral type from GCVS4.
The 7th and 8th row is the result of the Eddington/Plakidis test. Before the test is made the linear component of the diagram is removed and is then done with X<=15 and X<=5. This test is to see if the changes in the O-C is likely due to small random cycle-to-cycle fluctuations or a real change of the period. See Irregularities of period of long-period variable stars for more information about this test. In short ε is the average random error in the period and a is the average error in determine the time for maximum. The star falls outside the test if the term 2a2 have a big negative value and could be a sign of real period changes.

From the O-C the period of the stars over time were also calculated and plotted and can be found here. The diagrams are the same as the link Per under each star, but on a separate page.